Non-H98 crusade, contd.

[Keean Schupke]

ross at soi.city.ac.uk wrote:

>On Sat, Feb 26, 2005 at 08:00:22PM -0500, ajb at spamcop.net wrote:
>  
>
>>Quoting ross at soi.city.ac.uk:
>>    
>>
>>>Indeed.  Of all the extensions implemented by both GHC and Hugs, the only
>>>ones that seem ready are
>>>
>>>- rank 2 type signatures, and
>>>
>>>- polymorphic components for data constructors (giving them rank 2 types).
>>>      
>>>
>>Off the top of my head:
>>
>>- multi-parameter type classes
>>    
>>
>
>Reasonable in themselves, but limited in usefulness without some scheme to
>deal with overlapping instances, which doesn't seem settled at this time.
>  
>
In the HList paper we show that any overlapping instance can be 
eliminated with the use of a single constraint (that would have to be 
provided by the compiler: TypeEq).

Further I think functional dependancies (without overlapping instances), 
and undecidable instances are perfectly well understood. (incoherent 
instances would join overlapping instances and not be included).

So I would add:

- Multi-parameter type classes with functional dependancies (with no
overlapping instances allowed)

    Keean.